In some coastal areas, large quantities of beach-cast macroalgae can accumulate and are usually considered waste and disposed of. However, due to their biofunctional and nutritional properties, they have great potential as a new source of raw materials. Increasing population growth has made the search for alternative raw materials with valuable nutritional properties urgent; here, beach-cast macroalgae could provide great potential. Our research goal was to characterize the nutritional profile of 12 beach-cast seaweed species from the Brazilian coast to assess their potential valorization. A considerable number of nutritional compounds was observed, such as ash (6.5–59.3%), total dietary fibers (22.1–65.8%), proteins (5.1–21.5%), and carbohydrates (31.4–81.0%), with an expressive abundance of minerals, free amino acids, and fatty acids. Spatoglossum schroederi and Alsidium seaforthii showed protein contents of 21.5 ± 0.2%, 19.7 ± 0.1%, and high amounts of total dietary fiber of 59.2 ± 0.4%, 61.7 ± 4.9%, respectively. The overall profile suggests that beach-cast seaweeds are suitable for nutritional and other bioeconomical purposes, to which different species with different characteristics contribute. Contamination of these seaweeds with unwanted toxic compounds like micropollutants was not studied. However, this must be considered before they are used for human consumption.

Chlorophyll a and carotenoids are important pigments in photosynthesis. Several studies have been published describing extraction and analysis protocols of these pigments, mainly in vascular plant species. This study standardizes an extraction and analysis protocol of these substances in Gracilaria tenuistipitata var. liui, a red seaweed. Apical portions grown in vitro were triturated in liquid nitrogen. Extracts were prepared in 1.5 mL solvent and centrifuged. Quantitative and qualitative analyses of pigments were performed by UV/visible light spectrophotometry and high performance liquid chromatography (HPLC) and HPLC coupled to mass spectrometry (HPLC-MS). The parameters assessed were: minimum biomass, best extraction solvent, and number of extraction steps. Methanol was the most efficient solvent, and 50 mg fresh biomass was the amount of sample indicated, submitted to one single extraction step. No significant differences were observed in levels of these pigments by UV-visible light spectrophotometry and HPLC. However, HPLC or HPLC-MS are required to identify the different carotenoids present in this seaweed species.

Kappaphycus alvarezii is one of the most farmed algae globally. It is used almost exclusively for the carrageenan industry, although there is increasing interest in its biotechnological application as a natural product with biological properties. This cultivated species produces different strains with distinct chemical and physiological properties. Despite this, K. alvarezii has been marketed as a single biomass. The aim of this study was to evaluate differences in antioxidant capacities among green, red, brown and G11 strains of K. alvarezii cultivated in southeastern Brazil, assessed by Folin–Ciocalteu reducing potential, DPPH, ABTS and FRAP assay methods. Methanolic and aqueous extracts yielded from 2.67% to 3.43% and 26.25% to 32.90%, respectively. Nevertheless, methanolic extracts showed higher total phenolic content (40.80 mg GAE 100 g⁻¹ DW to 58.49 mg GAE 100 g⁻¹ DW) than aqueous ones (7.77 mg GAE 100 g⁻¹ DW to 12.51 mg GAE 100 g⁻¹ DW), and a similar trend was found for DPPH (7.15% to 31.21%), for ABTS (60.29% to 100.39%), and for FRAP (27.24% to 95.95%). Antioxidant activity of aqueous extracts was lower than 17% for all spectrophotometric assays. The green strain had the highest index of antioxidant capacity, suggesting that this strain may be suitable as a natural source of antioxidants. This is the first report evaluating antioxidant potential of four strains of K. alvarezii, supporting the need for further research to identify and select for its value as a viable natural antioxidant source.